644400660973 has 2 divisors, whose sum is σ = 644400660974. Its totient is φ = 644400660972.

The previous prime is 644400660947. The next prime is 644400660983. The reversal of 644400660973 is 379066004446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 378296343364 + 266104317609 = 615058^2 + 515853^2 .

It is a cyclic number.

It is not a de Polignac number, because 644400660973 - 2¹⁷ = 644400529901 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644400660913) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322200330486 + 322200330487.

It is an arithmetic number, because the mean of its divisors is an integer number (322200330487).

Almost surely, 2^644400660973 is an apocalyptic number.

It is an amenable number.

644400660973 is a deficient number, since it is larger than the sum of its proper divisors (1).

644400660973 is an equidigital number, since it uses as much as digits as its factorization.

644400660973 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2612736, while the sum is 49.

The spelling of 644400660973 in words is "six hundred forty-four billion, four hundred million, six hundred sixty thousand, nine hundred seventy-three".